Siren



FIG. 1 is a perspective view of a siren showing our new design;

FIG. 2 is a front view thereof;

FIG. 3 is a back view thereof;

FIG. 4 is a top plan view thereof;

FIG. 5 is a bottom plan view thereof;

FIG. 6 is a left side view thereof; and,

FIG. 7 is a right side view thereof.

The broken lines included illustrate portions of siren that form no part of the claimed design. 

CLAIM The ornamental design for a siren, as shown and described. 